The present invention relates to an improved method for direct metallization of non-conductive substrates. Included under the term direct metallization is a method in which a non-conductive substrate surface, such as a plastic surface, is activated by corresponding pretreatment steps to roughen the surface with a noble metal/metal-colloid containing aqueous formulation, whereby noble metal/metal-colloids are deposited on the substrate surface to be metallized. By subsequent treatment of the thus activated substrate surface with a metallic salt solution, which contains a metal cation reducible by an oxidizable metal ion of the colloidal formulation, the oxidizable metal ion of the colloidal formulation is replaced on the substrate surface by the metal of the metallic salt solution and forms a conductive layer on the substrate surface, which can serve as a starting point for subsequent metallization by electroless or electrolytic plating. In particular, a direct metallization process differs from conventional methods for metallizing non-conductive substrates by not treating the activated substrate surface with an accelerator solution and a subsequent chemical deposition of first metal layer, such as a nickel layer. By omitting these additional process steps and the associated economic and environmental advantages, the direct metallization has become an important method in the field of plating on plastics.
Corresponding methods for the direct metallization are known, for example, from EP 1734156 and corresponding US 2006/0280872 or EP 0 538 006 and corresponding U.S. Pat. No. 5,376,248. For example, European Patent Application EP 0 538 006 discloses a method for direction metallization, in which the substrate is activated with an activator solution comprising a palladium-tin colloid and following the activation, is contacted with a post-activator solution, which contains a sufficient amount of metal ions which undergo a disproportionation reaction under the reaction conditions. The treated substrates subsequently can be then electrolytically copper-plated for example in an acid copper electrolyte. EP 1734156 A1 discloses a method for direct metallization, in which likewise a non-conductive substrate is activated after a corresponding pre-treatment with metallic salt containing activator solution and a first conductive layer is formed on the thus activated substrate by means of a suitable metallic salt solution, on which a subsequent metal deposition can take place.
A disadvantage of the methods known from the state of the art is that on the one hand relatively high noble metal/metal-colloid concentrations must be used in the activator solutions, which leads to higher costs based on the associated high noble metal concentration and on the other hand, only certain plastics can be metallized by means of such methods.
Based on this prior art, it is therefore the object of the present invention to provide an improved method for direct metallization of non-conductive substrates, in which on the one hand smaller noble metal concentrations can be used in the activator solution, and on the other hand, a greater number of plastics can be metallized reliably.
This problem is solved by a method according to the novel method of the invention, preferably using a novel alkaline conductor solution, as described herein. Further refinements of the method and the alkaline conductor solution can be found in the following description and the dependent claims.